Observation of dimer excited-state dynamics in the double proton transfer reaction of 7-azaindole by femtosecond fluorescence up-conversion

Femtosecond time-resolved fluorescence of 7-azaindole dimer in hexane was measured at room temperature by using the up-conversion method. The measurements covering a wide visible wavelength region revealed that the fluorescence consists of two rapid decay components (τ1 = 0.2 ± 0.1 ps, τ2 = 1.1 ± 0.1 ps) and a long-lived component attributable to the tautomeric fluorescence (τ3 = 3.2ns and λmax = 490 nm). The two decay components were assigned to the fluorescences from two dimeric excited states which are successively populated in the relaxation process prior to the double proton transfer reaction. The dynamics of the excited-state proton transfer as well as assignments of the dimeric excited states is discussed.